Telephone system



Aug. 24, 1943. c. D. KoEcHLlNG TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet l Aug. 24, 1943.

c. D. KOECHLING TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet 2 lll-IlI /NVE/vrof? C. D. KOECHL/NG- ATTORNEY Aug. 24, 1943. c. D. KoEcHLlNG TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet 3 /NVENTOR By C. D KOE CHL /NG Aug. 24, y1943.r l c. D. KoEcHLlNG 2,327,436

' TELEPHONE SYSTEM v Filed July 22, 1942 9 Sheets-Sheet 4 /NVENTOR CD. KOECHL/NG il l l v d ArToR/VEV Am@ 249 i943., c. D. KOECHLENG 2932?43@ TELEPHONE SYSTEM I Filed July 22, 1942 9 sheets-sheet 5 FIG. 5

INTERMEDIATE GROUP TRAFFIC REG. CCT

/NVNTOR C. D. KOECHL /NG Bv l Q0" f f ATTORNEY Aug. 24, 1943. c. D. Kor-:CHLING TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet 6 /Nl/E/w-OR C. D. KOE CHL /NG ATTORNEY C. D. KOECH LING Aug. 24, 1943.

TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet 7 HMM M /NVENI'OR C. D. KOE C HL /NG a LV1- ATTORNEY Aug. 24; 1943. c. D. KoEcHLlNG TELEPHONE SYSTEM Filed July 22, 1942 9 Sheets-Sheet B /NVENTOR By C. D., KOECHL//VG 'Arron/vn Aug. 24, 1943. c. D. KOECHLING rPEIJEPIIONE SYSTEM Filed July 22, 1942 9 sheexssheet 9 ATTORNEY /M/ENTOR C. D. KOE CHL/NG Patented Aug. 24, 1943 TELEPHONE SYSTEM Charles D. Koechling, Floral Park, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 22, 1942, Serial No. 451,863

4 Claims.

This invention relates to telephonesystems and particularly to private branch exchange systems wherein the lines are interconnected by automatic switches,

In large capacity private branch exchanges it f is common practice to have an 'accompanying manual board by means of which incoming central office calls can be properly extended to the wanted subscriber. It is also common practice to have certain lines serving important oflices answered by the operators. Furthermore, means are commonly provided Aso that any subscriber by dialing a special number may gain the services of an operator.

Where the capacity of a private branch exchange of this nature becomes large the limit of the capacity of the accompanying board is approached. This limit is xed by the capabilities of the operators and the size of the line appearances which she may reach. The present inven tion provides a means for increasing the capacity of a private branch exchange very much beyond the ordinary capacity of the accompanying manual board. In accordance therewith the operators only partially complete a connection manually. Instead of having a line multiple before the operators a connector multiple is provided so that in completing a connection the operator plugs into a line designated by a portion of the digits of the wanted line andA then dials the remaining digits. l

It is generally conceded that a four-digit system is about the limit to the capacity of a manually operated switchboard. Hence, where the capacity of a private branch exchange requires more than four digits, other means must be employed. According to the present invention, the

. manual board is provided with a plurality of outlets to each hundred group of subscribers lines so that in a five-digit system the iirst three digits are manually selected and the last two are dialed. The system, therefore, embraces connectors reached by switch trains and other connectors known as attendants connectors and the latter differ from the former in many respects. Since the operators use certain standard cord circuits, the attendants connectors must be made `to produce the signals therein that are usually given'when the cord is used for its ordinary purposes. Thus, the battery feed and ringing arrangements for the called subscriber are Still in the cord circuit and must, therefore, be eliminated from the connector and the connector must be further modified to allow the passage of these supervision.

currents freely from the cord circuit to the called subscriber. The connector must signal the cord circuit to the effect thatl the line terminals of the called line have been reached and thereafter signal the idle or busy condition of the line and later the fact that the called subscriber has answered.

Heretofore a so-called cord circuit has been used having a marginal relay in the sleeve circuit thereof. By this' means the cord circuit is able to distinguish between different kinds of lines. For instance, on'ordinary outgoing lines such as central oce trunks where dialing arrangements in the cord are required, a high resistance sleeve in the outgoing line is used and through the non-operation of a marginal relay such dialing arrangements are rendered effective. On other lines, such as ordinary subscribers lines no dialing is necessary but ringing current is needed. In this case the sleeve of the line is made of low resistance and so through the operation of the said marginal relay the cord circuit is so affected that the dialing circuit is rendered ineffective and the ringing circuit in its place is rendered effective. Such prior art arrangements merely distinguished between diierent types of outgoing lines and made suitable arrangements in the cord circuit to cooperate therewith. In this connection reference is made to Patent 1,866,260 granted July 5, 1932, to `King et al. and Patent 1,881,669 granted October 11. 1932 to King et al.

Other prior art arrangements used other j methods of discrimination between theV types of outgoing lines but used what is termed sleeve By Way of example, Patent 1,675,956 granted July 3, 1928, to L. F. Porter shows the use of a marginal relay in the sleeve of the cord circuit which responds to a supervisory signal in the form of a change in the resistance of the sleeve of the cooperatively associated circuit.

signal given by the called subscriber causes its different rate on the means provided in the cord circuit with the result that a different type flash is produced which will properly notify the operator that a different condition has been encountered. This might be termed a syncopated flash since the timing relation of the dark and light periods has been changed. Whereas, the normal flashingrecall signal consists or" roughly equal periods of light and dark, the new or syncopated signal consists of a prolonged period of light and a shortened period of dark.

A feature of the present invention is the use of such a syncopated signal to indicate a busy ccndition encountered by a local operators connector. A grounded sleeve indicating a busy line is translated into the operation of an interruptor in the l connector` circuit which periodically opens the tip and ring circuit to the cord circuit. f

Reference is made to the copending applications Serial No. L151,862 led in the name of I-l. H. v Abbott; and Serial No. 451,918 iled'in the naine of A. S. Martins on even date herewith, bothof which applications cover inventions based mainly on thesame disclosure 'as that herein set forth.

Other featuresv'will 'appear hereinafter.

The drawings consist of nine sheets of circuit diagram.

Fig. 1 is a schematic vcircuit diagram showing the general plan of operation and indicating the 'arrangement of the remaining iigures;

Figs. 2 and 3 placed with Fig. 3 to the right of Fig. 2 show a cord circuit and Fig. 4 placed below Fig.l 3 shows the operators telephone and .dial circuit `all used at the manual switchboard used in connection with a dial .private branch exchange;.

, Fig. 5 shows an outgoing trunk circuit cooperating with the cord circuit of Figs. 2 and 3 by means ,ot which the operator'may control the distant connectorsof Figs. Gand 7 Fig. 6 shows a distant connector over which K anwoperator may reach any one of a group of iny Fig.`7 s hows a similar circuit arranged for 'trunk hunting over which an operator may reach a group of liners arranged in subgroups;

Fig. lwshows. an operators connector cooperating with the cord circuit er Figs. zand 3 over which an operator may reach any on@ of 'a group of individual lines; and

Fig'9 shows a similar circuit arranged for trunk hunting over which an opera-tor may reach a group of lines arranged in subgroups.

^ -The system herein diseio'sed is dial private branch exchange systemso large that itis beyond f the capacityof the manualattendants board. It is common practice to supplement a dial private branch exchange system with a manual lattendants board where incoming calls are answered and Acertain other special service is given. Gen- 'elrally speaking, a manual board has aV capacity of about ten thousand lines or can handlejonly four digit numbers. yBut it is possible to 'employ 'a system oi -much greater lcapacity for private The present system is y'.

branchy exchange service. shown asa five-digit system, though it may b'e of even greater capacity. l

Since the number of lines to be served is-beyond the capacity of a manually operated switchboard the operator is not given direct access to any of Y then dials the last two digits thereof. Thusdby way of example, ii theV operator wishes'torestablishaconnection t'o line numbered 12345 she vpart of the present invention.

way 'of example.

will insert her calling plug into a jack designated 123 and then dial 45. By thus setting up a connection partly by a manual operation and partly by an automatic or dialing operation the operato-r at such a switchboard may reach any one of a number of subscribers more numerous than could be reached by conventional methods.

In Fig. 1 there are shown two ordinary private branch oscila-ngelines terminating in saiions I and 2, each equipped with a dial. These station lines appear in a line finder 3 and by dial control may operate a first selector 4, a second selector 5,

third selector 6 and a connector l all in conventional manner. Thus these stations may be interconnected by ordinary and well-known means.. As indicated in this schematic any one of such ordinary stations may dial O and reach an operator through an answering jack appearance 8. Such a stat-ion by dialing the digit 9 may reach a central oflice 9 over an outgoing trunk ID. In the same manner any one of these stations by dialing 8 may reach a distant private branch ex- 'change Il over atie line I2.

There may be provided certain special lines fo high ranking oilicials such as those terminating in stations I3 and M which do not Aappear in line inders, but, on the other hand, have special switchboard appearances I5 and 5-, respectively, so that outgoing service is on'a manual basis. These lines have appearances in the bankk of the Aconnectors so that they may be reached automatically. l

`Incoming central olice lines and tie lines have manual appearances such as l 'I and I8.

The operator may answer a call at any one of the appearances 8, i5, i3, il or I8 by of the answering plug 'I9 of the cord circuit 20 and by means ofthe calling plug 2| may establish 'connections to any one of the stations of the private branch exchange. t is understood, of course, that the 'operator may also yeiztend connec'tions to the central oc'e 9 andthe distant Dri- 'vat'e branchvexchange `I l, but these arrangements are well known and 'do not form any essential I It may also be 'noted 'that the distant private branch 'exchange if! maybe the 's'a'meas the distant private branch exchangejin'dicated'in the broken line rectangle fin the-lower Ar'ightborner of this ligure. In `the 'one case the tie `line ii? leading to the private V 'three-digit number distinguishing the jack 2l.

In the same manner 1 the operator may employ 'the jack'25 to'reach any' one of one hundred lines characterized by the same liirst three 'digits which Vdistinguishesthe jack 25. However, this connector '2l is arranged. for trunk hunting and Vif Adriven tothe properlev'el will automatically pick out the iii-st idle one `of (stations 28, y29 and 30 by CORD lCIRCUIT y it will appesi-hereinafter lthat the com circuit yshown in Figs. 2fand 3 is arranged toco- `operate with various lines provided with aY conziection to'b'attery-onthe sleeves thereof. When :the plug of the rear cord '31 is vinserted in the jack associated wi-thna lighted line lamp, 'such as that associated with jack f5 for instance, a

:2,327,436 lcircuit will be established irorn battery on the sleeve of the associated line circuit through the sleeve of plug 3| and thence in series through the windings ci relays 33 and 34 through a small positive battery to ground. Both relays 33 and 34 operate in this circuit though the relay 33 performs no useful function at this time. Relay 34 operated closes a circuit from ground through its `armature and front contact and the winding of relay 35 to battery whereupon relay 35 operates .and at its armature and back contact opens acircuit for relay 33. Through the operation of ,relay a `circuit is closed from the tip of the plug 3l, springs 2A and 3 of the ringing key 31, upper winding of relay 38, springs 4v and 5 of the key 39, armature i and front contact of relay 35, armature 3 and back contact of relay 43', up-

. per winding of relay 4I to ground. At the same `time ,a circuit may be traced from the ring yof plug 3l through springs 5 and 4 of the ringing key 31, lower winding' of relay 38, springs `I I and i3 oi key 39, armature 5 and back Contact of relay 43, the lower winding of relay 4I to battery.

Relays 33 and 4I both operate due to current flowing through the circuit just describedand over the bridge provided by the calling line circuit. For a clear understanding lof the nature `of such calling line circuit reference4 may be had to the application iiled by Basconi and Lamberty, Serial No. 438,580, April 11, 1942.

Relay 38 operated prevents the rear` cord supervisory lamp 32 from lighting while the re- Relay 43 operated establishes a circuit from ground, its armature and front contact through the winding of relay to battery, causing AVthe operation of relay 45. Relay 44 in operating establishes a circuit from ground, its armatureand iront contact, through the Winding of relay 43 to battery whereupon relay 4S becomes operated. A circuit may now be traced from ground, resistance 43, armature and front contact oi relay 33, armature I and back contactl of relay 49, the lower winding of relay 41, springs 3 and 3 of key 39, iront contact and armature 6 of relay 45 to battery. Relay v41 operates and `locks in a circuit from ground, springs 6 and 1 of key 33, armature 5 and front contact of relay 35, armature 2 and front contact of relay 41, the upper winding of relay 41, back contact and armature 3 of relay 5D, springs 8 andV 9 of key 39, iront contact and armature 6 of relay 45 to battery.

The operation oi relay 44 prevents the operation of relay 45 when relay 45Y is operated by relay 43. The purpose of this will appear herein* after. Relay 45 operated causes the front cord supervisory lamp 5I to light under control of relays 45, 52 and 53. Y A circuit may be traced lfrom battery, lamp 5I, front contact and armature 3 of relay 45, armature 6 and front Contact of relay back contact and armature I of re'- lay 54, back contact and armature of relay 52, resistance 55 to ground. The operation oi relay 45 also vopens a retardation coil bridge circuit across the tip andl ring of the rearcord V3i which, up to this time has been open at the With relay 45 operated contacts of relay 45.

lto the ring of plug 3I.

.armature 2.of relay 45. .moves the busy test lead 5S from the tip of the Afront cord, connects the tip and ring of the cord and relay 43 unoperated a bridge circuit may be traced from the tip of plug 3|, springs 2-and 3 of key 3l, upper winding of relay' 38, springs 4 and 5 ofkey 33, back contact and armature 2 of relay 45, front contact and armature 2 of relay 45, back Contact and armature 3 of relay 36, retardation coil 68, armature I and back contact of relay 41, armature 8 and back contact of relay 33, springs I0 and II of key 39, lower Winding of relay 38, springs 4 and 5 of key 31 This circuit, though closed by armature 2 of relay 45, is opened by Relay 45 operated rethrough the contacts of relay 51 and disconnects battery through resistance 53 from the ring of the front cord plug. Relay 45 operated connects the windings of relay 52 to the front contacts of relay 5l'. A circuit may be traced from the tip of.' plug 42 through armature 4 and front 'Contact of relay 45, armature 3 and front contact of relay 45, springs 4 and 3 of relay 51, armature 4 and front contact of relay 35 to one side of the source of ringing current 59. The ring conductor may be traced from the ring of plug 42 through armature 5 and front contact ci relay 45, armature 4 and front Contact of relay 45, armature 6 and back contact of relay 151 through the upper winding of relay 51, armature 3 and front contact of relay 35 to the other side of the source of ringing current 53 so that vringing current is now supplied to the tip land ring of the plug 42 with the upper winding of tripping relay 51 in series therewith.- The source of ringing current 59 represents the usual machine-ringing source and may be applied at intervals through an interrupter. During ringing part of the ringing current flows through condenser 53 in a circuit which may be traced lfroin armature 5 of relay 51 through armature 31and front contact of relay 41, armature 5 and front contact of relay 43, condenser 60, springs 5 and 4 of :front cord ringing key 6I, springs I3 and I2 of keys 39, springs 8 and 5 of talking key 52, armature 8 and back contact of relay 43, lower winding of relay 52 to battery and in Vparallel therewith through condenser G3, back contact and armature 1 of relay 40, armature 6 and back contact'of relay 40 and thence through the lower winding of relay 4I to battery. Through the connection of ringing current to the lower winding ci relay 4 I, a ringing tone is transmitted back to the calling station as an indication that ringing current is being connected to the called station line.

When the receiver called station is removed from the switchhook the tripping relay 51 operates. The relay 51 thereupon substitutes the winding of relay 52 to the tip and ring of the called line in place of the source of ringing current 59 and locks through its lower winding, its contact 2 and armature I to the front contact and armature I of relay 45. Relay 52, now in circuit with the called station, operates and causes the front cord supervisory lamp to be extinguished and the relay 54 to operate through its lower winding. The circuit for relay 54 may be traced from ground, resistance 55, armature and front contact of relay 52, armature 3 and back Contact of relay 53, lower Winding of relay 54, front Contact and armature 1 of relay 45 to springs 3 and 9 of key 39, front contact and armature E of relay 45 to battery. Relay 54 locks in a circuit from ground, normal contacts of armature 4 of relay 53, armature 2 and front contact of relay 54, upper winding of relay 54 through back contact and armature 3 of relay 50 to battery over the circuit hereinbefore described. Relay 54 therefore locks under control of relays 53, 45, and 46 and partly provides an operating path for relay 53.

From the foregoing we can summarize as follows: (A) Battery and ground for the calling station are furnished by the cord crcuit'through the windings of relays 4l and 38. (B) Battery and ground for the called station are furnished by the cord circuit through windings of relay 52. (C) The front and rear cords are coupled through condensers 53 and 64. (D) No bridge is connected across the tip and ring of the cord, except the ringing relay 5l which has no useful purpose at this time.

When the receiver is replaced on the switchhook at the calling station, relays 4I and 38 release causing relay 49 to operate under control of relays 59 and 33. The circuit for relay Ailmay be traced from battery, armature 6 and front CQrltaCt of relay 45, springs 3 and 8 of key 39, armature 3 and back Contact of relay 53, winding of relay 49 through the normal contacts of armature 2 oi relay 49, armature4 and front contact of .relay 4l, back contact and armature of relay 38, through resistance 48 to ground. Relay 4 9 operated locks through its iront Contact and armature 2, front Contact and armature 5 of relay 35 springs 'l and 6 of key 39 to ground. The rear oord supervisory lamp 32 is now energized in a circuit from battery, lamp 32, armature 2 and iront contact of relay 35, armature 4 and front contact of relay 49, resistance 48 to ground. The lighting of lamp 32 operates as a disconnect signal.

When the receiver at the called station is replaced on the switchhook relay 52 releases causing relay 53 to operate under control of relays 50, 46 and 45. A circuit for relay 53 may be traced from battery, armature 5 and iront contact of relay 45, springs 9 and of key 39, armature 3 and back contact of relay 59, winding of relay 53 through the normal contacts of armature 2 of relay 53, iront contact and armature l of relay 54, back contact and armature of relay 52 through'resistance 55 to ground. Relay 53 locks through its iront contact and armature 2 to the normal contacts of armature 4 of relay 5.51 to. ground. The operation of relay 53 Dow lights the front cord supervisory lamp in a circuit which maybe traced from battery, lamp 5l, front contact 'and armature 9 of relay 46, armature 5 and front Contact of relay 45, front contact and armature l= of `relay 53, resistance 55 to battery, This lighting of lamp 5l operates as a disconnect signal. The operation of relay 53 in open-ing the-.path of the lower winding oi relay 54 at itsy back contact and armature 3 thereupon opens. the original operating circuit of relay 54 but. this relay remains operated through its upper winding. When the plugs of the iront and rear cords arev withdrawnl from the associated jacks all operated relays release and the circuit is restored to normal.

FLASHING Rec/im Ii before the plugs of the fron-t and rear cords are withdrawn from the jacks the switchhook at the calling station. is operated and released to recall the attendant, the relays 4l and 3.3, will release and reoperate. Therelay 38 in releasing causes the operation of relay 43 in the manner hereinbefore described. Upon the reoperation'of relay 38 the rear cord supervisory lamp is now connected in a circuit which may be traced from battery, lamp 32, armature 2 and front contact of` relay 35, armature 4 and front Contact of relay 49, through the resistance 48 and in parallel therewith, the armature and front contact of relay 33, armature l and front contact of relay 49 to the hashing recall lead E5 which eentaily supplied interrupted battery to periodically shunt the lamp 32.v This causes the lamp to hash. The attendant then operates the talking and dialing key 62 causing relay 50 to operate which releases relay 49. Relay v49 released, stops the ashing of the lamp 32.

If the switchhook at the called station is operated and released, relay 52 releases and reoperates. Upon the release of relay 52 lrelay 53 is operated, as hereinbefore described. With relay 52 reoperated the front cord supervisory lamp 5| is connected in parallel with the hashing recall circuit G5 in a manner similar to that hereinbefore described so that lamp 5| now flashes. The'attendant then operates the talk and dial key 62 causing relay 50 to operate. Relay 53 operated releases relays 53 and 54. Relay 53 released stops the flashing of the lamp. When the tall: and dial key 62 is restored to normal, relay 5D releases and relay 54 reoperates, as described hereinbeiore.

The above description applies to the use of the cord circuit when a. connection is being made between two local lines as, for instance, a. connection between the stations I3 and i4. In the schematic shown in Fig. l it is not contemplated that the calling cord 2l will be used for directly calling a local substation though it is capable of thisuse in the manner above described.

It should be noted that both the answering and calling cords have two relays in their sleeve circuits, one of which is marginal. Thus, for instance, the sleeve of the answering cord has the two relays 33 and 34 in series, the relay 34 being marginal and only operating when a line sleeve of lower resistance is encountered. In the same manner the sleeve of the calling plug 42 has the relays 43 and 44 in series with it, the relay 44 being marginal.

It will be noted in the description to follow that the sleeve of the line leading to an attendants connector as, for instance, from the jack appearances 22 to 25, inclusive, has a high resistance when it is selected and maintains this high resistance until certain operations are completed. after which the resistance is lowered. Therefore en a call from a station to another station via an attendants connector the marginal relay of the calling cord will not be operated at rst.

When completing a call from an attendants trunk, such as that terminating in the jack 8, or from a manual station, such as those terminating in the jacks l5 and I6, to a station via an attendants connector, the operation when the call ls answered with the rear cord is the same as described hereinbefore. However, when the front cord is inserted in the. jack associated with an attendants connector relays 43,` 45 and 4G operate since the sleeve resistance is high. Relay 40 operated disconnects the. relay battery supply from, the rear cord but the calling station receives battery from the connector in the manner which will be described hereinafter. When the operators dial is moved on normal for the nrst digit the rear cord is fed battery and ground from the telephone and dial' circuit and the front and rear cords are separated in the dial circuit. The attendant then dials the two digits required to bring the connector to the desired line.

The attendants connector will cut through on the called line if it is idle and the battery and ground from the tip and ring of the connector will be removed. At this time the connector also changes the resistance on the jack sleeve from high to low. The change to a low sleeve resistance causes relays 44 and 46 to operate which in turn causes relay 40 to release. The release of relay 4I! reconnects relay 4I to the rear cord and separates the rear and front cords by condensers 63 and 64. The connector is held off normal under control of the sleeve after cut through and the tip and ring of the front cord are connected to the back contacts of the tripping relay 51 to transmit machine-ringing current to the called subscriber. Audible ringing tone is transmitted toward the rear cord through condenser 6D as hereinbefore described. Relay 45 closes the windings of relay 52 to the front contacts of the tripping relay 51 to supply talking battery to the called line after tripping relay 51 operates upon the response of the called party.

When the called station answers, relay 51 operates and relays 52, 53 and 54 function as described hereinbefore. The talking, signaling, supervision, disconnect and flashing recall will be the same as described hereinbeiore.

If the attendants connector is dialed to a busy line the sleeve becomes low in resistance and the battery and ground on the tip and ring of the connector are removed and replaced by a bridge intermittently applied. The ringing from the cord is tripped through this bridge. If the attendant has restored the talk and dial key 62 the intermittent bridge across the tip and ring will operate and release relay 52 starting the flashing recall signal on the front cord lamp. If the attendant has not restored the talk and dial key 62 she will receive an audible busy indication.

It is particularly to be noted that the interrupter in the attendants connector circuit which intermittently applies the bridge to the tip and ring of the calling cord 42 is of one-half the rate of the interrupter 55. By way of example, the interruptor capplies battery to the lead 65 at the rate of 120 impulses per minutes while the interrupter in the attendants connector circuit runs at the rate of 60 interruptions per minute. Since the interruptor in the attendants connector circuit operates the relay 52 it will therefore render the flashing recall circuit of this cord circuit ei'- fective on every other interruption thereof so that the effect is that the lamp 5I Will be lit approximately three-tenths of a period and dark the other seven-tenths thereof. The signal for the recall is a steady hashing at the rate of 120 interruptions per minute, While the signal for the encounter of a busy condition is this so-called syncopated signal wherein every other flash of the signal in its ordinary working is rendered effective. Since the interrupter of the attendants connector circuit and the interruptor 66 are both operated` from the same power plant they may both be on the same shaft and the relation between them may be ixed.

The operation of the cord circuit on a connection between a central oiice call and a station is as follows: The incoming central office call is answered with the rear cord 3| in the usual manner and the operation is different from that described hereinbefore in that` a high sleeve resistance is encountered which does not allow the marginal relay 34 Vto respond. Since the marginal relay does not respond, therefore relay 35 does not operate.

As a result a connection is established from ground, springs 6 and 'I of key 39, armature 5 and back contact of relay-35, front contact and armature of relay 33, winding of relay 33 to battery. As a result of the operation of relay 36 a connection may be traced from ground at the armature and back contact of relay 34, armature 4 and front contact of relay 35, winding of relay 4!) to battery and ground whereupon relay 40 becomes operated. The operation of these relays connects a bridge across the cord which may be traced from the tip of plug 3l, springs 2 and 3 of the ringing key 31, iront contact and armature 3 of relay 35, retardation coil 68, armature I and back contact of relay 41, armature 8 and front contact of relay 35, springs 4 and 5 ofv ringing key 31 to the ringT of plug 3 I. This bridge serves as a signal on the central oilice line that the call has been answered and will serve to trip ringing and perform the other usual functions required in a case of this kind.

When the front cord is inserted in the jack of an attendants connector relay 38 operates and causes the operation of relay 41 on its lower Winding.

A circuit may be traced from ground on the tip of cord 3l, springs 2 and 3 of ringing key 31, up-

per winding or relay 33, springs 4 and 5 of key S3, y

front Contact and armature 1 of relay E3, springs 6 and 8 of key 62, springs I2 and i3 of key 39,

lsprings 4and 5 of key 6l, back conta-ct and armature 4 of relay 45, front contact and armature 5 of relay 45, to the ring of plug 42 where it encounters battery in the circuit of the attendants connector. Likewise, a circuit may be traced from battery on the ring of cord 3 i, springs 5 and 4 of key 31, lower winding of relay 33, springs I I and Il] of key 39, front contact and armature `2 of relay 453, springs 5 and 3 of key E2, springs 3 and 2 of key 39, springs 3 and 2 of key 6I, back contactvand armature 3 of relay 46, front contact and armature 4 o1- relay 45 to the tip of plug 42 where it encounters ground in the circuit of the attendants connector. Relay 38 responds and closes a circuit from ground, resistance 48, armature and front contact of relay 38, armature l and back contact of relay 45, lower winding of relay 41, springs 3 and 3 of key front contact and armature 5 of relay 45 to cause the operation of relai7 4l'.

Relay 38 will release when the dial is moved on" normal but relay 45' will not operate and relay 41 will release since the talk and dial key 62 is operated. Moving the dial off normal separates the front and rear cords. The attendant then dials the two digits to direct the connector to the de sired line.V

The attendants connector cuts through on the called line if it is idle, removing the battery and ground from the tip and ring and changing the jack sleeve resistance associated with the front cord to a lower value. Thus relays 44 and 45 will operate but relay 4l] remains operated under control of relay 33. The tip and ring of the front cord are then connected to back contacts of tripping relay 51 for the transmission of ringing current. rThe calling lamp 5I will also light at this time.

When the called station answers the tripping relay 51 operates and closes through the tip and ring of the front cord. The ground that locks relay 51 operated also passes over lead 69 to the telephone circuit and causes a relay therein to operate and furnish talking battery to the called station until the talking key is restored by the attendant. When the talk and dial key 62 is restored to normal the battery and ground from the central office is fed through the windings of relay 3B to the called station. Relay 38 will operate and extinguish the calling line lamp at this time and relay 4l will operate, opening the short circuit about resistance 'l0 whereby less current from the central olice line is drained by the bridge and a greater amount allowed to flow to the called station. The operations in this connection may now be summarized as follows: (A) Talking battery for the called station is furnished from the central oiiice. (B) A highresistanoe bridge consisting of the Winding of retardation coil 68 in series with the resistance 'l0 is bridged across the tip and ring of the rear cord. (C) The supervisory relay 3B is under control of the called station.

When the receiver is replaced on the switchhook at the called station the circuit functions, as describe-d hereinbefore, except that relay 38 is under control of the called station and the operation of relay 49 causes the front supervisory lamp to light as a disconnect signal and short circuits the resistance l0, thereby decreasing the resistance of the bridge across the cord.

Flashing recall is controlled by relay 38 in conjunction with relays 41 and 49, as described hereinbefore. However, since relay 35 is not operated the supervisory lamp El of the calling cord is ilashed rather than the answering oord lamp 32.

If the called station is busy the sleeve becomes low in resistance and the battery and ground are removed from the tip and ring in the connector and replaced by a bridge which is intermittently applied. If the talk and dial key 62 has been restored to normal the application of this bridge will cause the supervisory relay 3B to operate and release, thereby starting the flashing recall signal on the front cord lamp. lf the attendant has not restored the talk and dial key on a busy connection she will receive an audible busy indication.

In the rst case, where the busy indication cornes in from the attendants connector circuit 'the bridge will be app-lied to the tip and ring at the rate of 60 interruptions per minute and this will so effect the flashing of the lamp 5l at the rate l2@ interruptions per minute that every other iash will be eliminated, resulting in what is spoken of as a synccpated signal in which the lairp 5l lighted for approximately three-tenths of a period and dark for the remaining seventenths.

TELEPHONE AND DIALING CIRCUIT ARRANGED Foa Usa WITH ArrENDANTs CONNECTORS Busy test When the tip of an associated cord, for instance, plug 42, is touched to the sleeve of a busy station line, tie trunk, attendants connector or trunk jack, ground or positive potential from the busy sleeve charges condenser El through a winding of the repeating coil l?. and resistance 13 to the fro-nt contact of relay '14, this relay being .energized through the transmitter 'l5 of the telephone set. This induces a busy click through the winding of the repeating coil l2 the attendants telephone receiver.

Talking When. the talk and dial key 62 of an associated cord circuit is operated the leads T6 to 80, inelusive of the telephone and dial circuit are connected to the cord circuit, thereby closing the tip, ring and receiver leads and providing a talking circ-uit for the attendant. The attendants transmitter circuit may be traced from ground, the right-hand winding of repeating coil 8|, through the tip of jack 82, transmitter l5, the tip of jack 83, the winding of relay 14 to battery. Speech currents from the transmitter l5 are then transmitted by the left-hand windings of repeating coil 8i, through the back contacts and armatures 2 and l of relay 84 to the talking conductors 85 and 8'5. The operators telephone receiver circuit may be traced from conductor through the bac-k Contact and armature of relay 8T, back contact and armature l of relay 84, the sleeve of jack the telephone receiver 88, the sleeve of jack 83, armature 3 and back contact of relay '84, the mid-point tap on the left-hand winding of repeating coil 8l through the condenser 89, back Contact and armature 4 of relay 84 to conductor i36 Through the back contacts and armatures of relay Sii this talking circuit is connected to conductors 'l and l?, leading to the front cord 42. rI'hrough the armatures and contacts of relays 9i and 92 this talking circuit is connected to conductors 'i8 and 79 leading to the tip` and lring of the rear cord 3i.

Dialing In order to dial on a cord circuit the talk and dial key 62 of the cord circuit is operated. When the dial is moved cri normal relay 93 operates in a circuit which may be tra-ced from ground, springs 2 and 3 of key 94, the off-normal springs of the dial S5, winding of relay 23 to battery. Through its front contact and armature 2 relay S3 short circuits resistance 9S. The opera-tion of relay 93 also results in the operation of relays 91, 8l and 9U. The circuit for relay 91 may be traced from battery, winding of relay 97, front contact :rnd armature 3 of relay S3 to ground. The circuit ior relay 8l' may be traced from battery, winding of relay 81, front contact and armature 4 of relay 93 to ground. The ground for the operation cf relay Sl may also be trace-d through the armature 5 and back Contact of relay 84, the lower winding of relay to battery. Upon the operation of relay 91 ground is extended from armature 2 oi relay 9i' and its iront contact through the upper winding of relay 90 to battery. With relay Si operated the attendants receiver is short circuited at the armature I and front contact of relay 9"! for a suilicient length of time to prevent an undesirable click when the dial restores after dialing the first digit. This also prevents the attendant from hearing transmission of the dial pulses. With relay Sil operated the attendants telephone circuit is disconnected from conductors 7G to 79. Through its armature 2 and front contact relay 90 causes the operation of relay 92. At this time a short circuit across conductors T5 and 11 may be traced from conductor 16, conductor 98, the contacts of the dia1 95, armature 2 and front contact ol relay 93, iront contact and armature 4 of relay 90 to conductor ll. The retardation coil 99 is short circuited through the front Contact and armature 4 of relay 92. The operation of relay 92 splits the cord circuit leaving the impulse springs of the dials connected to the front cord over leads '16 and Vi and battery and ground through the windings of relay |00 connected to the rear cord over the leads 'IS and '19.. Relay IUI) operates over the station loop or through the retardation coil bridge in the cord in case the receiver at the station hasv been replaced on the switchhook. Dial impulses are transmitted over the circuit to which plug 42 is connected in the usual manner. When the dial has completely restored relay 93 releases. With relay S3 released the short circuit is removed from the parallel combination of the resistance 96 and retardation coil 99 and relay El is released. The release of relay Sl removes the short circuit on the attendants receiver and releases the relay 90. Relay 90 released removes the shunt of the resistance 96 about the retardation coil 99 and closes the attendants talkingT circuit. The retardation coil 99 now holds the connection, the circuit being traced from conductor T6 through the impulse springs of the dial 95, the retardation coil 99, front contact and armature 4 of relay to conductor ll. VThe front and rear cords of the associated cord circuit are con` neet-ed through condensers IUI and |02 to enable the station to talk on the connection in case the attendant fails to restore the talkand dial key of the cord after dialing. When the talk and dial. key G2 vis restored relays mi) and 92 release.-

FRONT CORD INsEe'rEn 1N ArTENnANrs CONNECTOR JACK The circuit functions as describe-d above. Re-

lay |00 is connected to leads 'I8 and 'I9 after relay 92 operates and is held operated over the station loop if the rear cord is connected to a station. If the rear cord is connected to a centrai office trunk, battery and ground through the windings of relay IG!) will be connected respectively to ground and battery from the central oilice due to a reversal in the cord circuit and relay IBD will therefore be operated. When the dial returns to normal relays 93, S1 and S53 release but relay I remains operated holding relay 82, which in turn holds relay Sl' operated.

When the attendant has finished dialing the station number the attendants connector cuts througlrin a manner which will be hereinafter described; This action results ina reduction of the sleeve resistance so that marginal relay i4 now becomes operated, in turn operating relay 46. During the operation of thetalk and dial f key 62 a circuit is established from ground, springs 4 and 5 of key 94, springs and I2 of key 62 to the winding of relay 50 and thence to battery whereupon relay 50 becomes operated. Now upon the operation of relay 46 a circuit is established from ground. front contact and armature 5 of relay 4S, front contact `and armature 4 of relay 5l] to the Winding of relay I 03 which now becomes operated. Relay I b3 operated opens the circuit to relay I which releases and allows relays 92 and 81 to release. In this way al1 the relays in the dialing circuit restore to normal and leads 76 and VI of the cord are connected to leads I8 and 19.

Monitoring This telephone circuit is arranged with a position monitoring key. If the key S4 is operated and then the talk and dial key E32 of a cord circuit is operated the attendant can monitor on the particular cord whose key is operated. The

operation of the position monitoring key 94 removes ground from spring 4 thus allowing relay 5I) to become'released and at the same time causes relay 84. to become energized. Relay 84 operated connects the attendants telephone receiver across the cord through the repeating coil |04, the rest of the telephone circuit being disconnected frcrn the receiver at this time. The release of the position monitoring key releases relay 84.

Jacks 82 and 23 are for the use of the operator and jacks |95 and IBS are for the use of the supervisor.

OUrcoINc ATTENDANT TRUNK CIRCUIT 'ro ATTEND- ANT CoNNEcroR Ar DIsrANr PRIVATE BRANCH EX- CHANGE-FIG. 5

A plug seating circuit is provided to insure against preliminary impulses during plug-in. This comprises a pair of relays IDB and |09, the

. first of which is a two-step relay. When relay |08 is energized through its lower winding it will move its armatures 3 and 4 but will not move its armatures I and 2. This is indicated by the fact that armatures `I and 2 are shown heavy and armatures 3 and Il are shown light. When a plug, such as plug 42, is inserted in jack IU'I and the plug becomes fully seated, then a connection is made between the ring of the plug and the ring of the jack |91 which may be traced through armature 2 and back contact of relay |08. back contact and armature I of relay H8, the lower windingof relay |08 to ground. Since battery is supplied by the ring of the plug of the cord circuit, relay m8 moves its armatures 3 and 4. Thereupon a connection is made from posi` tive battery, winding of relay 44, winding of relay 43 and the Sleeve of the cord in cord circuit, Fig. through the sleeve of jack Ic'I, armature and front contact of relay |63, winding of relay |09 to battery. Relay I 09 operates and establishes a connection from battery, upper winding of relay Hi8, armature' and front contact of relay |08, arma-ture 3 and front contact of relay IUS, the

lower winding of relay |58 to ground. Thus the two windings of relay IDH are placed in seriesv and this relay thereupon fully operates and attracts all of its armatures.

In its normal condition a circuit is established from battery, through armature 2 and back contact of relay Ita, through the backcontact and armature 3 lamp IIS. Therefore, upon the operation of relay |53 this idle indicating lamp is extinguished; and the battery connection. is extended by arma-- ture 2 of relay E238 to its front contact to cause the lighting of the next idle `indicating lamp.

Upon the operation of relay |68 the tip conductor is extended over armature I and front contact of relay |88, the upper left-hand winding of repeating coil` |2I, back contact and armature 4 of relay I IQ, the upper winding of relay |I2 to ground. jack itil is extended from armature 2 and fro-nt contact of relay 08, the lower left-hand winding of repeating-coil IRI, back contact and armature E of relay II il, the lower winding of relay I I2 to battery. Due to a reversal in the cord circuit hereinbefore explained, relay H2 becomes operated. The operation of line relay |I2 ccnnects the windings of the polarized relay I|4 to the distant connector circuit which has a relay facing the line to this trunk circuit. This connection may be traced as follows: from ground, through the lower winding of relay II4, armature of relay H8 to the idle indicatingl In a similar manner the ring of 2 and front Contact of relay I I2, the lower righthand winding of repeating coil i 2 l, conductor I i5, back contact and armature Il of relay |23 to conductcr IE5 and a similar ircuit from battery, the upper winding of relay H5., armature and front Contact of relay H2, the upper right-hand winding of repeating coil Il! I, conductor I I6, baci; contact and armature I of relay |23 to conductor |24. Relay i I operates in this circuit and causes the operation of relays II'I and H8. A, rcircuit may be traced from battery, winding of relay I il, back Contact and armature 3 of relay IIS, armature and left-hand Contact 0f relay H12, armature and back Contact of relay H5, armature 'l and back contact ci relay H0 to ground. Relay H'l, in operating, connects ground through its armature 2 and front Contact to the winding o relay H8.

When the attendant dials, relay H2 follows the dial pulses and opens the line to the distant connector each time it releases. The polaiaed relay lid follows the dial pulses as repeated by relay l I2 but the slow-release relay Il holds operated.

When dialing is completed the distant connector circuit inserts a high resistance into the line causing relay H4 to release. The release of relay H4 causes the release of relay H1 which, due to the slow releasing characteristic of relay H8, results in the o-peration of the cut-through relay HEB. A circuit for this relay may be traced from ground, armature and front contact of relay m9, armature 2 and front contact of relay H8, back Contact and armature I of relay H1, the winding or relay H0 to battery. Relay H0 locks through its armature 5 and front contact and the front contact and armature of relay |69 to ground.

The. operation of relay ID causes the resistance in the sleeve lead to change from high to low. Up to. this time the winding of relay |99 which has a high resistance is connected to the sleeve of jack IGT! but upon the operation 'of relay H0 a lower resistance |26 is placed in parallel with the winding of relay |09 so that the marginal relay M in the cord circuit now becomes operated. 'Ihe operation of relay H0 also connects a condenser |28 across the middle of the side of the repeating coil facing the distant connector and prepares a circuit for connecting the windings of relay H4 with polarity reversed to the leads of the distant connector through normally closed contacts of relay H2 and the windings 'of the differential relay H9. The operation of relay HD. opens the circuit of relay H2 so that this now releases. Relay HS also prepares a circuit for giving a closure to the cord circuit through the contact of the polarized relay H4.

The change in the sleeve resistance to the cord circuit resulting in the operation of the marginal relay 54S causes the cord circuit to send out ringing to this` trunk. The ringing current causes relay |22 to operate which results in the operation of relay |23, thus causing a clear path from the tip and ring of the jack |91 to the line conductors |24 and |25, respectively.

When the called party answers or when the distant connector connects a low resistance ground to the ring lead as a line-busy indication during the ringing interval, the tripping relay in the cord circuit operates and removes the ringing current, causing relays |22 and |23 to release. The release of relay |23 again places the polarized relay Iflin circuit to operateover the station loop if the line-is-idle. I-f, on the other hand,

the line is busy and the operation just described. has been caused by a low resistance ground to the ring lead, then the diiierential relay I I8 will be unbalanced as a busy indication and instead of connecting a bridge across the tip and ring of jack Iil, will now connect interrupted ground to the ring of jack Ill'l, leaving the tip thereof open. In case only relay H4 operates as a signal that the called party has answered, a circuit may be traced from the tip of jack lill', armature and front contact of relay |03y the upper lefthand winding of repeating coil I2 I, front contact and armature 'l of relay HD, back contact and armature oi relay H9, left-hand contact and armature of relay I4, armature 3 and front contact of relay lo, the lower left-hand winding of repeating coil IEI, front contact and armature 2 of relay |68 to the ring of jack |01; In case the signal coming from the distant connector is a low resistance ground on the ring, thereby causing the relay HSB also to operate, a connection may be traced from the ring of jack |01, through armature 2 and front contact of relay |68, the

lower left-hand winding of repeating coil |2|,`

front contact and armature 3 of relay ID, armature and left-hand contact of relay I4, armature and front contact of relay H9 through retardation coil irl and interrupter |28 to ground. Upon the first open period of this circuit, the dashing recall circuit in the cord will be prepared for operation and then put into operation upon the next closure through the interrupter |28. Thereafter the signal displayed in the cord circuit will be modified by the interruptor |28. Since this is of one-half the rate of the interrupter causing the flashing recall signal, the result will be a totally different kind of visual signal in which cuit so that the relation between the two is Vfhen the called line is idle and the ringing has been tripped, conversation may take place with the transmission battery for the called party furnished through the windings of relays H4, H9 and the repeating coil |2,|, The contacts of relays Hi! maintain a closure toward the cord circuit and relay H4 will receive switchhook ashing from the called party to the cord circuit so that a flashing recall condition may be set up in the ordinary manner by the subscriber reached through the distant connector.

'When the plug is removed from the jack, relay |09 releases causing the release of relays |98 and IIB. The release of relay HG causes the release of relay H'I and relay H4, except that this latter relay may have `already released due to the called party hanging up. The release of relay H'i causes the release of relay H8 which causes the idle indicating lamps to light and restores the circuit from the lower winding of relay IDB to the ring of the jack |61 so that it can operate on the next call.

Upon the seizure of the circuit shown in Fig. 5 and the operation of the line relay H2 thereat, battery and ground are connected through` the windings of relay ||4 to the conductors |24, |25 which extend to the upper and lower Windings, respectively, of line relay |29. Relay |29 operates from battery on the tip and ground on the ring of the trunk circuit and causes the operation of the irst slow relay |30 in preparation for pulsing.

On the first open period relay |29 releases and establishes a circuit from its armature I and back contact, through armature I and front contact of relay |39, springs 6 and 3 of the vertical offnormal spring combination 13|, through the windings of slow-release relay |32 and the vertical magnet-l |33 to battery. Relay |32 operates before the vertical magnet steps the switch, opens the circuit of relay |34- and closes its own locking circuit to spring 5 of the vertical offnormal springs |3|. When the switch steps and the vertical olf-normal springs operate, the original operating circuit for relay |32 and magnet |33 will be opened but a substitute circuit through the armature of relay |32 will be closed in its place without interrupting the stepping circuit. When the line relay |29 reoperates the vertical magnet releases, but relay |32 being slow toy release holds until the end of the train of impulses comprising the rst digit.

The switch thus continues to step vertical until the end of the train of impulses when the operation of relay |29 releases relay |32.

Gn the second digit, when relay |29 releases, I

relay |34 and the rotary magnet |35 operate. The circuit may be traced from armature and back contact of relay |29, armature and front contact of relay |39, springs (i and 5 of the vertical off-normal spring combination |3|, armature and back contact of relay |32, armature 4 and back contact of relay |33, through the winding of relay |34 to `battery and in parallel therewith through armature 4 and back Contact of relay |31 and the winding of rotary magnet |35 to battery. The rotary magnet and relay |34 are in multiple and the latter relay being slow to release remains operated during pulsing while the rotary magnet steps the switch to the desired terminal.

Testing the liuc-Zine busy When the switch is on the line to which it has been dialed and before the slow-release relay |33 releases, the sleeve of the called line is connected to relay |38. A circuit may be traced from battery through the Winding of relayl |38, iront Contact and armature 2 of relay |34, sleeve brush |33 to the sleeve terminal of the called lin-e. thereby operating relay |33. When relay |34 releases, relay |38 locks through the normal contacts of armature 2 ol relay |34, front contact and armature 2 of relay |38, armature 3 and front contact oi the rst slow-releasing relay |39 to ground.

Relay |38, operated, opens the circuit of relay 3? and operates relay |33. This circuit may be traced from battery, winding of relay |36,

armature 3 and back contact of relay |34, front .i

contact and armature 3 of relay |38 to ground. Relay |36 operated, (l) opens the circuit of relay |33 and the circuit of rotary magnet |35, (2) removes the line relay |29 from the tip and ring, thereby causing the release bf relay |29, and (3) connects high resistance relay |30 through the armature and back contact of relay |4| and the iront contact and armature of relay |33 to the tip wire |24 and high resistance relay |42, through armature 5 and back contact of dit On a busy line the sleeve will be grounded, r.'

relay |36 to the ring conductor |25.

relay |43, the front contact and armature 4 of Relay |42 operates to ground on the ring at the distant end of the trunk and holds the rst slow relay |30 operated.

Removing the line relay |29 from the tip and ring is a signal to the trunk at the distant private branch exchange to prepare to ring or to receive busy ashes and when the trunk is thus prepared it reverses battery and ground to the connector circuit. Relay |42 then releases and relay |49 then operates. Relay M0 closes resistance |46 across the windings of relay |29 which thereupon operates and holds the first slow relay |30 operated. Relay |29 also completes the circuit to relay |43 through the armature 2 and front contact of relay |29, armature 3 and front contact of relay |36, to ground. Upon operating, relay |43 establishes a connection from ground, armature 2 and front contact of relay |43, front contact and armature of relay |33 to the ring conductor |25 extending to the outgoing trunk circuit, Fig. 5, where it results in unbalancing the differential relay ||9 for the purposes hereinbefore described.

When the called line is idle, the sleeve brush |39 will encounter a battery connection instead of ground and relay |34 in releasing at the end of the rotary stepping movement connects relay |31 to the sleeve brush. This circuit may be traced from sleeve brush |39 through armature 2 and back contact of relay' |34, upper winding of relay |31, back contact and armature 2 of relay |38, armature 3 and front contact of the rst slow relay |30. Relay |31 becomes sulciently energized in this circuit to move its armature which closes a circuit from ground, armature 2 and front contact of relay |39, front contact and armature 2 of relay |31, lower winding of relay |31, through rotary magnet |35 to battery. This causes the full energization of relay |31 and at the same time stops further action of the rotary magnet. Relay |31 connects direct ground forward to the line circuit sleeve through its front Contact and armature 6 to hold the cut- 01T relay of the called line and to busy the terminal to other switches. Relay |31 also opens the original energizing circuit for the rotary magnet and opens the release path through its armature 1. Through its armatures and 3 relay |31 partially closes the tip and ring conductors to the called station.

Upon the release of relay |34 and the operation of relay |31 a circuit is established from ground through the front Contact and armature 5 of relay |31, back contact and armature 3 of relay |34 to the winding of relay |36. As hereinbefore described, relay |33, upon operating, removes the line relay |29 from the tip and ring and closes the two high resistance relays |49 and |42, respectively, to the tip and ring of the trunk. y Relay |42 holds rst slow relay |39 operated until battery is reversed by the trunk circuit at the lprivate branch exchange. Relay |42 then releases and relay |49 operates. Relay |40 again causes the operation of the line relay |29 to complete the circuit to relay 43 which now operates. Relay |43 operated connects the tip and ring of the trunk from the distant private vbranch exchange to the tip and ring of the called station. The tip conductor |24 may be traced through the upper winding of the supervisory relay |44, through armature and front contact of relay |43, front Contact and armature of relay |31 to the tip brush |45 of the connector which is now inassociation with the tip of the called line Elli. The ring conductor |26 may be traced through the lower winding or relay lklll, armature l 'and iront )Contact of relay Ifl, front Contact and armature 3 of relay |37 to the ring brush M8 of the connector leading to the called subscribers station lill. Relay 143, in operating, opens the circuit of relay |62 but relay M6 is still connected to the tip 'so that the line relay |26 remains operated.

During the ringing of the station from the distant private branch exchange, -relay '|60 holds to the ringing ground on the tip. Relay 1M, whose lower winding is in series with the ring, may operate on the alternating current and operate relay lill. This will open the winding of Vrelay Mil but its lower rcontacts perform the same 'function as the lower contacts of relay l'll' so 'that the line relay |25 remains operated 'to hold the connection. n l/Vhen the vcalled station answers, ringing is tripped and relay IM operates on the station loop to remove "relay |156 from the c'oiinec'tion and hold the connection'through the operation of relay Ml as described. Upon disconnection 'by the called station relay llll releases and causes relay 'lill 'to release, but 'relay 'Ulli vthen operates to ground on the 'tip to hold the switch.

When the cord is pulled down at 'the private branch exchange after 'the called station disconnects, relay |66 will release thus releasing the line relay l2@ and 'the irilt "slow 'relay |36. lRelay |3S,`in releasing, opens the circuit for relay I3? and now a circuit may be traced from ground, armature l and back contact of relay |`2 9, armature l and back contact of relay liti), 'back Contact and armature 'l of relay |37, springs 'I and 2 'of the vertical off-normal spring 'combination '|'3|, to release magnet |156 and battery. Release 'magnet 'lit is operated and causes the 'brushes V|45, Hi8 and 'lill-i to leave their position in connection with the terminals of the called line, Thus, the switch is returned to normal. The 'release 'of relay `|3l 4causes 'the release of relay '|36 and the release 'oi relay |25 causes the release or relay '|2l3. On disconnection bythe attendant from a busy connection, relay M6, in releasing, releases the line relay l2@ and the nrs-l', slow relay |56. Relay E66 then releases relay |38 which, in turn, releases both relays |36 'and T43. With relay |39 released, the release magnet operates to restore the switch to nor-mal.

CONNECTOR CIRCUIT-ROTARY HUNTING-Foa CotirLErING FROM ArrsN'DANr Ar DrsrANr Parwirs BRANCH EXCHANGE ro STATION LINES-FIG. '7

The operation ci this connector is in many respects similar `to the operation of the connector in Fig. 6. When the attendant at the distant private branch exchange selects this trunk, the line rela-y l@ operates from battery on 'the tip and ground on the 'ring of the trunk circuit at the distant private exchange. Relay "|56, operated, operates the nrst slow `relay l5! 'which prepares the 'circuit for pulsing.

On the first open period relay |56 'releases operating the second slow relay |52 Yin series with the vertical inagnet |53, 'through the springs 'of the vertical oil-normal contact combination 'l5'4. Relay |5l being slow to release will 'remain'operated during pulsing. Relay `|52 operates before the vertical magnet 'steps the switch, opens the'circuit of relay |55 and closes its own locking circuit to the ,vertical offnormal springs. When the switch steps 'and the vertical orf-normal springs operate, 'the original operating circuit of relay |52 will be opened-but 'the holding path will be completed without interrupting the stepping icircuit. When 'the line relay |56 reoper'at'es, the "Vertical magnet releases but relay |52 being slow to release holds until the end lo'f the digit. The switch thus continues to step vertically until the end of the digit when the opera-tion o'f relay |56 releases relay |52. On the second digit when the line relay |56 releases, relay '|55 and the rotary magnet operate. Relay |55 being lslow to release holds Iover pulsing while the rotary mag- -net steps the switch to the desired line terminal which may be either an individual line or the iirst lof a group of lines.

Before relay 55 releases at the end of rotary stepping a path is closed from the sleeve wiper |56 of the `connector switch through armature 2 and front contact of relay |55, armature and back Contact of relay |57 to the winding vof relay |58 and thence to battery. A busy line will have -grbund on the sleeve which will operate relay 58. When relay |55 releases, relay |53 locks to the sleeve Vground through its armature 4ffl 'and front Contact and the normal contacts of `armature 2 of relay |59 to the sleeve wiperl5t. Relay |53 at this time causes the operation of relay |63 in a circuit from battery, winding of relay |66, back Contact and armature l of relay |55, front 4contact and armature '2 of relay y|58 to conductor |6| supplied with ground over armature 2 and front contact of the first slow relay |'5|. Relay |65 operated, (1) opens the circuit of relay |55 'and the circuit olf the rotary magnet |62 (2) removes the line relay |56 from the tip and ring which now releases, (3) connects high resistance relay |63 tothe ring conductor |25 and'hi'gh rcsistance relay |64 to the tip conductor |24, and (4) closes a circuit from relay |65 which may 'be 'traced from battery, the winding of relay |65, 'ar-mature and ba'ck'contac-t ol' the rotary magnet |62, normal contacts of armature l2 of relay |65, iront contact and armature 5 of relay 58, Jarmature 6 and front contact of relay |69, armature VI and back contact of relay |59, front contact and armature of relay |58, to wiper |66 or the connector. Relay 4|63 holds 'to ground on the ring at the distant end of the trunk and holds relay |5| operated.

If the busy line -is the nrst terminal `in a group of lines, the bank terminals lcooperating with brushes |56 and |66 will be strapped together as indicated in the second group -of bank terminals where direct connection is `shown between bank terminals |61 and |63. Thus, the busy potential of terminal |671 will be connected -to terminal |68 Aically until an -idle terminal 'is -f-ound or the last line-of the group is encountered. Relay 68 being slow to release holds during -this stepping and will remain operated so long -as busy -lines are encountered.

The switch 'will not step 'beyond the last terminal in the group since the terminals |69 and |16, cooperating with wipers "I 56 and x| 66, respectively, a're not strapped together 'and there Will rbe no operating circuit for relay |65 as'de'scribed above. Relay I 58 remains operated from ground on terminal |09 and an operating path for relays |59 is found from battery, through the winding of relay Ii to ground on the sleeve. During rotary stepping on terminals other than the last, relay |58 does not operate since it is bridged across the leads which are strapped together on these bank terminals. Relay |58, operated, locks itself and relay |58 to ground on conductor ISI and opens the circuits leading to wipers |55 and Iii. Relay |55 does not operate in series with relay |59.

The operation of an individual busy line is the same as described for the last line of a group except that there is not rotary hunting.

Removing the line relay from the tip and ring as described above is a signal to the trunk that the distant private branch exchange to prepare to ring or to receive a busy indication and when the trunk is thus prepared, it reverses battery and ground to the connector circuit. Relay E83 then releases and relay |55 operates. Relay Hill closes resistance |1I across the windings of the line relay li which operates and holds the iirst slow relay I5I. Relay |51] completes the circuit for relay H2 which closes ground to the ring of the trunk to the distant private branch exchange as a busy indication. This last connection may be traced from ground, front contact and armature 5 of relay E12, armature E and back Contact of relay |51 to the ring conductor |1125. This, as described hereinbefore, operates the diiierential relay H9 in the outgo-ing trunk circuit and causes the so-called syncopated signal to be displayed in the cord circuit.

If the first line of the group or an individual line is idle, relays |58 and |55 will not operate. `When relay releases, the upper winding of relay E51 is closed to the sleeve wiper |50. Battery through the cut-oir relay on the sleeve bank operates armature 5 or" relay 51 which closes a circuit for the lower winding thereoflto completely operate relay |51. Relay |51, operated, grounds the sleeve wiper |55 to busy the line and to hold the cut-off relay operated partially closes the tip and ring oi' the line to the trunk, opens the rotary magnet, release magnet and the circuit of relay |58 and prepares the circuit of relay |12 which will become eiiective upon the reoperation of the line relay |50.

When relay |611 operates on battery reversal from the trunk circuit at the distant private branch exchange, relay |50 operates to complete the circuit for relay |12. Relay |12, operating, removes relay |83 from the ring of the trunk, closes the tip and ring of the trunk to the tip and ring of the station, and locks independently of the contacts of relay |50. During ringing from the distant private branch exchange relay IEM holds to ringing ground on the tip. The supervisory relay |13, whose windings are in series with the line tothe called station, may operate on ringing current and operate relay |14. Relay |14 opens the circuit of relay its but since its armature I and front contact perform the same operation as the armature and front contact of relay |64, relay |50 will be maintained operated to hold the connection.

When the called line answers and ringing is tripped, relay |13 operates on the station loop to remove relay Il from the connection and to hold the connection through the operation of relay |14 as described. On disconnection by the called station, relays |13 and |16 release but relay |64 holds the switch.

. line relay |50 and the first slow relay |5I.

, `When theswitch in rotary hunting over busy lines as described above steps to an idle line, relay |58 releases because of absence of busy potential on the sleeve but relay which had operated from relay |58 remains operated through locking contacts to insure that the battery and ground from the line relay |50 are not again connected to the tip and ring. Relay |51 operating on the idle line as described above cannot operate until relay |58 releases and it is, therefore, necessary to lock relay |60 operated.

When the cord is pulled down after the station disconnects, relay |64 releases releasing the Relay I5I releases relay |51 which operates the release magnet |15 Vto restore the switch to normal and releases relays |60 Iand |51 On disconnection by the attendant from a busy connection, relay |64 releases relay I5| which operates the release magnet to restore the switch to normal. Relays |58, |59, |60 and |12 also release.

CONNECTOR CIRCUIT For. COMPLETING reoivr A'rrENDANr To STATION LINES-FIG. 8

A plug seating circuit is provided to insure against preliminary impulses during plug-in. When the plug is fully seated battery on the ring of thecord operates relay |11 to operate its armature 4 only. This closes the sleeve of the jack tothe upper winding of relay |18. Relay |18 operates and extinguishes the idle indicating lamp |19. Normally the circuit may be traced from ground through lamp |18, springs 5 and 4 of the vertical oli-normal spring combination |80, back contact and armature 2 of relay |13. Upon the Voperation of-relay |18 this circuit is opened and battery is extended through armature 2 and its front contact to the corresponding armature of the next corresponding relay |8| for operating the idle indicating lamp circuit. The operation of relay |18 also closes a circuit through the lower winding of relay |11 0to fully operate this relay. Relay |11, fully operated, opens its own upper winding and closes the tip and ring of jack |16 to ground and battery, respectively, through the windings of the line relay |82. Relay |11 also grounds lead |83 for purposes to be described hereinafter,

The line relay |82 operates from a bridge in the cord circuit and energizes relay |84 which locks `to `ground through its armature 3 and front contact, armature l and back contact of relay |85 to ground on conductor |83. The circuit is now ready for pulsing. On the iirst opening from the dial relay |82 releases operating relay |85..` in series with the vertical magnet |21. Relay |86 operates before the vertical magnet steps the switch, opens the circuit of relay |88 and closes its own locking circuit to the vertical off-normal springs. When the switch steps and the vertical off-normal springs |80 operate, the operating path of relay |86 will be openedbut the holding path will be completed Without interrupting the stepping circuit. When the line relay |82 reoperates the vertical magnet releases but relay |86 being slow to release holds until the end of the digit. The switch thus continues to step vertically until the end of the digit when the operation of relay |82 releases relay |86.

On the second digit the line relay |88 and the rotary magnet operate. The circuit for this operation may be traced from ground, armature 3 and back contact of relay |89, armature and back contact of relay |82, armature I and front con- 

